350-501 Practice Test 13 — 15 Questions

Question 1

A network engineer notices that BGP-LU prefixes learned from an eBGP neighbor are not being installed in the MPLS forwarding table (LFIB). The BGP table shows the prefixes with the correct label. The IGP route to the neighbor is reachable. What additional configuration is needed?

Accepted Answer

Set `label mode per-prefix` under the BGP neighbor or address-family. For BGP-LU to install labels into LFIB, the `label mode` must be set to `per-prefix` or the router must have `mpls bgp forwarding` enabled. Without enabling label allocation per prefix, BGP-LU prefixes are not programmed in LFIB. The other options are not directly related.

Answer

Enable `no bgp default ipv4-unicast`

Answer

Configure `mpls ldp autoconfig` on the interface

Answer

Add `allowas-in` to accept routes with AS-path containing own AS

Question 2

A network engineer needs to ensure that a specific customer's traffic is not adversely affected by other customers' traffic in a shared MPLS core. Which technology should be used?

Accepted Answer

QoS policies on PE routers with shaping and policing. Option C is correct: QoS on the PE routers can shape and police traffic per customer. Option A (MPLS TE) is for bandwidth optimization, not per-customer guarantee; Option B (VLANs) is layer 2; Option D (iBGP) is routing.

Answer

iBGP route reflectors

Answer

MPLS Traffic Engineering

Answer

802.1Q VLANs

Question 3

A company is connecting two sites using MPLS L3VPN. The PE routers are running both LDP and Segment Routing (SR-MPLS) in the core. The CE router at Site A cannot reach the CE at Site B. On the PEs, the VRF routes are present. Which command would you use to verify the MPLS forwarding path for the VPN traffic?

Accepted Answer

show mpls forwarding-table vrf VPN-A 10.1.1.0. To verify the MPLS forwarding path, including the label stack used for VPN traffic, the command `show mpls forwarding-table vrf ` shows the outgoing labels and next hop. `show ip route vrf` only shows the IP route without labels. `show mpls ldp bindings` shows LDP bindings but not per-prefix forwarding. `show bgp vpnv4 unicast labels` shows the VPN labels but not the transport labels.

Answer

show mpls ldp bindings

Answer

show ip route vrf VPN-A 10.1.1.0

Answer

show bgp vpnv4 unicast labels

Question 4

Which statement about the use of MTU in an MPLS network is correct?

Accepted Answer

MPLS adds a label stack to packets, reducing the payload MTU.. Option C is correct. MPLS adds a label stack header, which reduces the effective MTU for payload. If the packet size exceeds the MTU of the outgoing interface after label imposition, fragmentation may be needed. Option A is false because MPLS can fragment (though not always desirable); Option B is false because MTU is not automatically increased; Option D is false because MPLS adds overhead.

Answer

MPLS does not affect the MTU because labels are part of the header.

Answer

MTU must be increased on all MPLS interfaces.

Answer

MPLS eliminates the need for IP fragmentation.

Question 5

Which THREE steps are required when configuring MPLS L3VPN on a PE router? (Choose three.)

Accepted Answer

Create a VRF definition. To configure MPLS L3VPN, you must: create a VRF (step A), assign an interface to the VRF (step B), configure BGP to exchange VPN routes (step C). Step D is optional (route-target export/import is done via route-map or configuration). Step E is done on CE, not PE.

Answer

Configure BGP on the CE router to advertise routes to PE

Answer

Configure route-target import/export using route-map

Question 6

An ISP is designing a new core network using MPLS-TE. They require very fast failure detection for link and node failures to minimize traffic loss. Which two technologies should they combine? (Choose two.)

Accepted Answer

MPLS-TE Fast Reroute (FRR). Option A and D are correct. BFD provides fast failure detection (sub-second), and MPLS-TE Fast Reroute (FRR) provides local protection with backup tunnels. Option B (LDP) does not provide fast detection; Option C (OSPF) alone is too slow; Option E (LSP ping) is for troubleshooting.

Answer

OSPF with hello timers set to 1 second

Answer

LSP Ping and Traceroute

Answer

Label Distribution Protocol (LDP)

Question 7

Which routing protocol is used between CE and PE routers in a typical MPLS L3VPN deployment?

Accepted Answer

BGP. The CE-PE routing protocol can be any: static, RIP, EIGRP, OSPF, or BGP. However, in service provider networks, eBGP or OSPF are common. The question asks for typical; BGP is often used for multi-homing and scalability.

Answer

RIP

Answer

EIGRP

Answer

IS-IS

Question 8

In a Layer 3 MPLS VPN, a customer site that is part of VRF RED is unable to communicate with another site that is also in VRF RED. The 'show ip bgp vpnv4 vrf RED' command shows the routes, but the router does not install them in the routing table. Which configuration element is most likely missing?

Accepted Answer

The route-target import on the receiving PE.. Option B is correct because route-target import on the receiving PE is required to install VPNv4 routes into the VRF. Option A is incorrect; export is for sending routes. Option C is incorrect; LDP is used for label exchange but not for VRF route installation. Option D is incorrect; BGP sessions between PEs are usually in place if routes are seen.

Answer

A BGP session between PEs.

Answer

The route-target export on the receiving PE.

Answer

An MPLS LDP session between PEs.

Question 9

Which LISP feature allows a device to register its location to a mapping system so that another device can find it?

Accepted Answer

ETR. Option B is correct: In LISP, the ITR (Ingress Tunnel Router) performs mapping lookup, but the ETR (Egress Tunnel Router) registers mappings with the MR/MS (Map-Resolver/Map-Server). Option A (xTR) is both; Option C (MR) resolves mappings; Option D (PITR) is proxy ITR for non-LISP sites.

Answer

Map-Resolver (MR)

Answer

Proxy ITR (PITR)

Answer

xTR

Question 10

Which TWO statements accurately describe MPLS LDP label distribution and autoconfiguration? (Choose two.)

Accepted Answer

LDP can be configured to allocate labels only for specific prefixes using label filtering.. LDP allocates labels for every IGP prefix by default. It uses the Transport address (usually loopback) to establish sessions. Option D is incorrect because LDP can also use targeted discovery.

Answer

LDP uses hello messages sent to multicast address 224.0.0.2.

Answer

LDP sessions are always established using the physical interface IP address.

Answer

LDP label allocation is per interface by default.

Question 11

A service provider is troubleshooting BGP route selection between two eBGP peers. The router receives a prefix from Peer A with local preference 150 and AS path length 3. From Peer B, the same prefix has local preference 100 and AS path length 2. Which route will be preferred?

Accepted Answer

The route from Peer A because local preference is higher.. BGP selects the route with highest local preference first. Peer A has local preference 150, which is higher than Peer B's 100, so Peer A's route is preferred regardless of AS path length.

Answer

The route from Peer A because it has a higher weight.

Answer

Both routes are equally preferred and will be used for load balancing.

Answer

The route from Peer B because AS path is shorter.

Question 12

During multicast troubleshooting, the command 'show ip mroute' shows that the RPF neighbor for a particular (S,G) entry is incorrect. What is the most likely cause?

Accepted Answer

The unicast routing table does not have a route back to the source.. The RPF neighbor is determined by the unicast routing table towards the source. If the unicast route points to a different next-hop than the actual multicast path (e.g., due to asymmetric routing or incorrect unicast route), the RPF check fails and the multicast tree is not built correctly.

Answer

The multicast routing protocol is not enabled globally.

Answer

TTL threshold is set too high on the incoming interface.

Answer

IGMP snooping is disabled on the switch.

Question 13

Based on the exhibit, which OSPF network type is configured on this interface?

Accepted Answer

Point-to-Point. The output shows 'Network Type POINT_TO_POINT', so the interface is configured as point-to-point.

Answer

Non-Broadcast

Answer

Broadcast

Answer

Point-to-Multipoint

Question 14

Which QoS mechanism marks packets at the edge of the network to classify traffic into different service classes?

Accepted Answer

Marking. Classification and marking are used to identify and mark packets with a specific class of service (e.g., DSCP, IP Precedence). This occurs at the edge before the packet traverses the core.

Answer

Queuing

Answer

Shaping

Answer

Policing

Question 15

Segment Routing with TI-LFA (Topology Independent Loop-Free Alternate) provides fast convergence. Which statement accurately describes TI-LFA?

Accepted Answer

TI-LFA computes a backup path that is guaranteed to be loop-free and topology independent.. TI-LFA computes a backup path using segment lists that are guaranteed to avoid the failed link/node, and it works regardless of the network topology (topology independent). It is based on SR-MPLS or SRv6.

Answer

TI-LFA only protects against link failures, not node failures.

Answer

TI-LFA uses a pre-computed backup tunnel signaled via RSVP-TE.

Answer

TI-LFA requires BFD to detect failures.